[Bug c++/12789] New: [tree-ssa] Miscompilation of small program

[bangerth at dealii dot org]

PLEASE REPLY TO gcc-bugzilla@gcc.gnu.org ONLY, *NOT* gcc-bugs@gcc.gnu.org.

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=12789

           Summary: [tree-ssa] Miscompilation of small program
           Product: gcc
           Version: tree-ssa
            Status: UNCONFIRMED
          Keywords: wrong-code
          Severity: normal
          Priority: P2
         Component: c++
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: bangerth at dealii dot org
                CC: gcc-bugs at gcc dot gnu dot org

This small program
---------------------------
#include <fstream>
#include <string>

void foo (const int i) {
  std::ifstream in("irrelevant");
  std::string line;
  if (i == 1) return;
  foo (1);
}

int main () {
  foo (0);
}
---------------------------
segfaults on running when compiled with the tree-ssa
branch from
  gcc version 3.5-tree-ssa 20031024 (merged 20031017)
It doesn't segfault with mainline from the same day, though.
Assuming that the code in libstdc++ is the same on the two
branches, this means that something is being miscompiled. This
could, theoretically also include a miscompilation in libstdc++
itself, since I can't get around using parts of it, but it 
strikes me as odd that I need the tail recursion in foo() to
actually trigger the bug in the program. Maybe it is just
some interaction of the tail recursion and the stack space/
constructors/exception handling details of the objects in use
in this function that make this happen, so this could actually
be simple to track down than it looks like.

W.